The invention relates to a method for controlling a transmission of a motor vehicle.
The continuously increasing demands on the functionality of automatic transmissions by shifting quality requirement, the need of more spontaneity, the constantly enlarging number of gears to be shifted and the higher economy requirements on automatic transmissions are taken into account in the practice by an adaptive control for automatic transmissions. With such an adaptive transmission control (AGS), the generally pursued end is to adapt the gear selection to the behavior of the individual driver and, at the same time, taking into consideration the environmental conditions and the concrete driving situations. Thereby the control comfort should be improved, among other things, by reducing both the required engagements by the driver and the shifting frequency in sporting driving mode. Besides, in the smooth driving mode, the fuel consumption to be lowered, the same as the driving safety increased on even roads, for example.
One adaptive transmission control used in the practice engages, for example, four shifting programs which upwardly and downwardly enlarge the band width of the programs formerly used. Besides, for automatic selection of the shifting programs and gear selection according to situations, functions have been introduced which can be classified in four function blocks: a driver type recognition, an environment recognition, a driving situation recognition and a manual engagement. In the driver type recognition, a conclusion as to the driver""s wish is reached from the evaluation of characteristic accelerator pedal actuations, one of four shifting programs being chosen from the results of the analysis. Via the functions of the environment recognition elevated traction resistances can be found which are caused, for example, by high loading or road gradients. In addition, low adhesion coefficients between tires and road can be detected. In both cases, shifting programs are called up which are optimized with regard to the special situations. The recognition of the driving situation reacts to actual events, such as driving downhill, and makes gear shifts possible which diverge from instructions stored in the form of characteristic lines. The function block xe2x80x9cmanual engagementsxe2x80x9d further offers to the driver the possibility of influencing the gear selection via the selector lever and the program selector caliper.
It is disadvantageous, however, that even though an optimization of the gear selection of the automatic transmission can be carried out via the adaptive control, an adaption of the gear shift itself, that is, effected in the automatic transmission cannot be directly carried out.
In order to be able to satisfy a requirement of adaptation of a gear shift to tolerances of component parts of shifting elements of the automatic transmission, it has been changed over in the practice to taking into account, the influences of the tolerances of component parts of the shifting elements of the transmission during a gear shift. It is here established, firstly, how a transmission or a shifting element of the automatic transmission affected with tolerances of component parts behaves during a gear shift under minimum and maximum specific tolerance. With the aid of this observation, a shifting cycle is established wherein, with the shifting cycle based on the tolerances of component parts, there are tuned and stored in an electronic control unit pressure curves for a filling pressure abutting on a shifting element during a filling phase and a differential pressure abutting on the shifting element during a shifting phase which constructively acts upon the filling pressure, ultimately produces the engagement of the shifting element.
In view of the multiplicity of influences appearing on all operating points due to the tolerances of components, scatterings of operating parameters of the automatic transmission and other influences, it is not possible with the former steps to deduce the correct reaction in order to optimize a gear shift that follows an evaluated gear shift. From speed reactions at the input or output of the transmission or with the aid of pressure and regulation values of the transmission control, it is not possible to deduce adaptation values which can be corrected on the respective operating point of the automatic transmission shifting inaccuracies due to tolerances of components and wear of the shifting elements, the same as temperature influences and scatterings of the operating parameters.
Therefore, the problem on which this invention is based is to make a method for control of a transmission of a motor vehicle available which, for each of the different influences which impair a gear shift, a separate adaptation can be carried out from which can be deduced the respective right reaction for an optimization of a subsequent gear shift.
According to the invention said problem is solved with a method according to claim 1.
With the aid of the inventive method in which for each gear shift, at least one adaptation of the pressure curves of the control pressure of the shifting elements for compensation of tolerances of components, preferably of the shifting elements taking part in the gear shift, and one for compensation of influences determinant of the shifting quality on the shifting elements are alternatively carried out for different shifting strategies or kinds of shifting, it is quickly possible to compensate tolerances and wear of component parts of the shifting elements, for example.
It is essential to the invention that the filling parameters of the clutches can be determined or evaluated both during a normally developing gear change and also by special pressure curves controlled outside gear changes. The filling operation of a clutch, therefore, must not indispensably be connected with a gear shift of the transmission to be carried out, but can also be carried out in the form of predetermined test pressure curves (test pressure phase) in predetermined operating points of the transmission, the pressure curves not leading to gear change. Advantageous test pressure curves are derived from shifting parameters. A rapid filling pressure test pulse makes it possible to easily determine and adapt tolerances of the hydraulic clutch control, of the clutch release play and of the seal ring friction of the clutch piston. A filling pressure test pulse makes it possible to easily determine and adapt tolerances of the piston recoil forces of the clutch. Combinations of rapid filling pressure test pulse and charge pressure test pulse obviously can also be used. The test pressure curves are advantageously designed so that no speed reactions of the drive train, negatively traceable for the driver, occur outside the gear shifts.
By the further provided targeted optimizing adaptation of the shifting quality, it is possible to obtain more shifting comfort and an increased spontaneity of the automatic transmission since, with the adaptation for compensation of influences determinant of shifting qualities of the shifting elements, it is possible to take, into account on the relevant operating point, operating parameters such as the transmission temperature, friction values, loadings and aging of the shifting elements and to adapt to the influences of a subsequent gear shift.
The inventive method is universally utilizable for automatic transmissions, automated mechanical transmissions and continuously variable automatic transmissions where at least one shifting element is electrohydraulically actuatable.
By virtue of the alternation of the adaptations, the results of one adaptation is scarcely susceptible to error in itself other adaptations and by the separation of the influences affecting the gear shift and the subsequent interaction for the adaptation results, an altogether quickly reacting, accurate total adaptation system leading to the correct reaction can be created.
It is also an advantage that additional evaluation memories or safety factors can be eliminated, since the adaptation of the pressure curves for compensating the tolerances of components of the shifting elements prevent erroneous interpretations in the evaluation of a gear shift.
It is thus possible with the inventive method to carry out an immediate, quick and accurate adaptation of the operating point for the next gear shift and signals of the individual factors that negatively affect the shifting quality and spontaneity of the transmission can be quickly and very precisely compensated purposefully and by the adequate evaluation.
In an advantageous design of the inventive method, the adaptation of the pressure curves for compensating tolerances of component parts of the shifting elements can be carried out starting from a minimum preset tolerance range of the shifting elements taking part in the gear shift and used for different shifting strategies or kinds of shifting. There results a quick optimization of the shifting cycle of a subsequent gear shift independently of which shifting strategy or which kind of shifting is the basis.